The idea of heat death stems from the
second law of thermodynamics, of which one version states that
entropy tends to increase in an
isolated system. From this, the hypothesis implies that if the universe lasts for a sufficient time, it will
asymptotically approach a state where all
energy is evenly distributed. In other words, according to this hypothesis, there is a tendency in nature towards the
dissipation (energy transformation) of
mechanical energy (motion) into
thermal energy; hence, by extrapolation, there exists the view that, in time, the mechanical movement of the universe will run down as work is converted to heat because of the second law. The conjecture that all bodies in the universe cool off, eventually becoming too cold to support
life, seems to have been first put forward by the French astronomer
Jean Sylvain Bailly in 1777 in his writings on the history of astronomy and in the ensuing correspondence with
Voltaire. In Bailly's view, all planets have an
internal heat and are now at some particular stage of cooling.
Venus, for instance, is still too hot for life to arise there for thousands of years, while
Mars is already too cold. The final state, in this view, is described as one of "equilibrium" in which all motion ceases. The idea of heat death as a consequence of the laws of thermodynamics, however, was first proposed in loose terms beginning in 1851 by Lord Kelvin (William Thomson), who theorized further on the mechanical energy loss views of
Sadi Carnot (1824),
James Joule (1843) and
Rudolf Clausius (1850). Thomson's views were then elaborated over the next decade by
Hermann von Helmholtz and
William Rankine. originated the idea of universal heat death in 1852. In 1852, Thomson published
On a Universal Tendency in Nature to the Dissipation of Mechanical Energy, in which he outlined the rudiments of the second law of thermodynamics summarized by the view that mechanical motion and the energy used to create that motion will naturally tend to dissipate or run down. The ideas in this paper, in relation to their application to the age of the
Sun and the dynamics of the universal operation, attracted the likes of William Rankine and Hermann von Helmholtz. The three of them were said to have exchanged ideas on this subject. In 1862, Thomson published "On the age of the Sun's heat", an article in which he reiterated his fundamental beliefs in the indestructibility of energy (the
first law) and the universal dissipation of energy (the second law), leading to diffusion of heat, cessation of useful motion (
work), and exhaustion of
potential energy, "lost irrecoverably" through the material universe, while clarifying his view of the consequences for the universe as a whole. Thomson wrote: The clock's example shows how Kelvin was unsure whether the universe would eventually achieve
thermodynamic equilibrium. Thomson later speculated that restoring the dissipated energy in "
vis viva" and then usable workand therefore revert the clock's direction, resulting in a "rejuvenating universe"would require "a creative act or an act possessing similar power". Starting from this publication, Kelvin also introduced the
heat death paradox (Kelvin's paradox), which challenged the classical concept of an infinitely old universe, since the universe has not achieved its thermodynamic equilibrium, thus further work and
entropy production are still possible. The existence of stars and temperature differences can be considered an empirical proof that the universe is not infinitely old. ==Current status==